As this kind of conventional shutter unit, an optical shutter is described in Patent Document 1, and a shutter mechanism of a laser processing machine is described in Patent Document 2.
With the optical shutter described in Patent Document 1, a cylindrical shutter unit which rotates around an axis line that is orthogonal to an optical axis of a laser beam is disposed on the optical path of the laser beam, and a through hole is formed along the optical axis of the laser beam on the side wall of this shutter unit. In this optical shutter, when opening the optical path of the laser beam, the through hole is positioned on the optical axis of the laser beam so as to pass the laser beam therethrough, and, contrarily, when closing the optical path of the laser beam, the through hole is moved from the position on the optical axis of the laser beam so as to block the laser beam with the side wall of the shutter unit.
Further, with the shutter mechanism of the laser processing machine described in Patent Document 2, a through hole and a reflective mirror are respectively provided to a position facing each other across the center of rotation in a laser beam blocking plate which rotates around an axis line that is parallel to the optical axis of the laser beam. In this shutter mechanism, when opening the optical path of the laser beam, the through hole is positioned on the optical axis of the laser beam so as to pass the laser beam therethrough, and, contrarily, when closing the optical path of the laser beam, the reflective mirror is positioned on the optical axis of the laser beam so as to reflect the laser beam toward a damper.    Patent Document 1: Japanese Patent Laid-Open Publication No. H7-193300    Patent Document 2: Japanese Patent Laid-Open Publication No. H10-34368